Carbon arc feed



July 10, 1951 R. L. GARMAN ET Ax. 2,550,155

CARBON ARC FEED Filed OCT,- 26, 1950 Non Y MW

Parental July 1o, i951 CARBON ARC FEED Raymond L. Garman and John K.McKendry, Pleasantville, N. Y., assignors to General PrecisionLaboratory Incorporated, a corporation of New York Applicationctober 26,1950, Serial No. 192,214

1o claims. l

This invention relates to an improved carbon arc control and moreespecially to a control for automatically regulating the position inspace of the luminous crater of the positive electrode of adirect-current arc lamp. The invention is applicable toautomatically-controlled arc lamps employed in searchlights and for usein the projection of mctionpictures or in the illumination of studios,and to automatically-controlled arc heaters.

In direct-current arc lamps and arc heaters the major portion of theemitted light and heat is generated at or closely adjacent to thepositive carbon crater. and the generated heat or light is applied tothe desired location by means of some form of optical concentratingsystem.

As the positive carbon is consumed it must be v fed or advanced, notonly to maintain the arc at its desired length but also to keep thepositive crater at its optimum optical position. It is well recognizedthat this advancement of the positive carbon is accomplished withgreater accuracy and ease by automatic means than by manual means, withthe radiation from the luminous crater itself made to actuate suchautomatic positioning means through a light-sensitive or heat-sensitivedevice.

The use-of light-sensitive devices for the automatic control of theposition of the positive carbon crater of an'arc has usually requiredthe use of a sensitive and relatively expensive ampliiier. The instantinvention, however, employs simple means for accomplishing this object.The light from the luminous positive crater of the are is directed upona dual photoconductive cell which controls a gas discharge tube. Theinternal resistance of this` tube is thereby varied and the variation ismade to control the speed of an electric motor geared to advance thepositive carbon. The speed of this advance is thus simply controlled bythe position of the positive arc crater.

The general objective of this invention is to provide improved means forcontrolling the position of the positive carbon of a direct-current arclamp, including photosensitive means and discharge tube ampliiicationmeans.

More speciiically the objective of this invention is to provide meansfor automatically keeping the crater of Ythe positive carbon of adirectcurrent arc lamp in the proper operative position, the light ofthe positive crater of the arc being employed through photosensitivemeans to control the position-regulating means.

A further understanding of the invention may 2 be secured from thefollowing detailed description together with the accompanying drawings.in which:

Figure 1 illustrates a circuit embodying the invention.

Figure 2 illustrates an alternative circuit employing a hot-cathodeamplifying tube.

Referring now to Fig. 1 an electric arc lamp is represented by apositive electrode I I and a negative electrode I2, between which an arcis maintained supplied from direct-current terminals I 3-I3. Due to theaction of the arc, a crater I4 is hollowed in the end of the positiveelectrode II, and most of the light and heat emitted by the lamporiginates at this point by the arc action. The positive crater isautomatically and precisely held in a iixed position. counteractingconsumption of the positive carbon,.by the apparatus of this invention,and the negative carbon I2 is advanced to maintain a constant arc lengthby any conventional means which is not shown, but which may be manual ormay be controlled by the current flow through the arc.

A portion of the light emitted at the positive crater I4 is directed bymeans of a simple system, consisting of a slit I6 between the opposedparallel edges of two plates I1 and I 8, upon a photoconductive cellrepresented by the symbol I3. This cell may be of any type but as vanexample a lead sulphide cell is here illustrated. This cell isconstructed by applying a very thin coating or film of lead sulphide tothe interior surface of a transparent glass tube. Two conductors 2I and22 are secured to the glass and conductively connected to the film atdiametrically opposed locations, and a third conductor 23 is secured andconnected to a medial location of the lm. These three electricalconnections to the lead sulphide film are in the form of parallel lines,represented in Fig. 1 by the terminals 24, 26 and 21, the distanceseparating terminals 24 and 28 being the same as that separatingterminals 26 and 21. The lead sulphide iilm resistance is inverselyrelated to the in-l tensity of the light falling upon it, and it is thisproperty that is here employed.

The terminals 24 and 21 are connected through amorce be employed toaccomplish the saine results as are accomplished by this circuit. lit ispreferred, however., to employ a gas discharge tube ampliiler because orits simplicity and high amplidcation, the cold cathode type beingdepicted in Fig. l at I3.

Alternating potential is applied to the gas triode anode circuit fromtill-cycle supply terminals 34-34 and a transformer 3G, so that anodecurrent ilows during the positive halt of each cycle,under control ofthe starting time thereof by the grid 34, and the current is inrruptedduring negative haii-cycles. l limiting resistor 3l is placed in serieswith the anode circuit to limit the maximum current ilow and a couplingresistor 38 is also included in series.

This resistor 36 is common to another circuit including direct-currentpower terminals ill-39a motor held 4 i, a neld rheostat i2 and a nxedfield resistor 43. The direct-current terminals are also connected to amotor armature and rotor @d associated with the iieid di. A double-polesingle-throw switch @d is arranged so that when in the "manual positionit is open and when in the automatic position it is closed, one poleshort-circuiting the resistor lli) and the other 'pole closing thecircuit to the primary winding oi the transformer tb. In operation oithe circuit, light from the positive crater M oi the burning arc lampfalls through aperture l@ upon an area ci the surface oi thephotoconductive cell lil. lf egual areas on opposite sides oi the medialconnection represented by the terminal 2o are equally illuminated, theresistance between terminals il and 26 equals the resistance betweenterminals 2G and 2l and the potential or the terminal 2G is half-waybetween the potential at the terminal 2d and the potential at theterminal 2l. But since the terminals 24, 25 and 2l are connected t@ theanode 3i, control grid lit, and cathode 32 respectively oi the gas tube33, the potential oi the grid iid is, under this condition, halt-waybetween the apodo and cathode potentials. The characteristie or thecold-cathode tube is such that its current dow is then or anintermediate amount. Component circuit magnitudes are such that thiscurrent is secured almost entirely by self-rectilication oi' thealternating current output of the transiormer so, when its primaryswitch is closed. This alternating current is prevented from nowingthrough the circuit including the motor iield @l because oi itsinductance.

The direct-current news from o9-3@ oi the power supply through thearmature lill, energizing it, and through a relatively low resistancecircuit including the held li and the resistors 36, di and d3 in series,when switch at is open. Circuit magnitudes are selected to be such thatwhen the switch GG is open, the held rheostat di may be adjusted tooperate the motor di at a speed that moves the positive carbon il at arate that approximately compensates its rate ci consumption. 'llhus thecrater ld will remain. at about the same point in relation to theaperture i6.

lin order to control position ci the crater ld automatically., theswitch d6 is closed, energizing the gas triode 33 and short-circuitingthe resistor d3. The latter action increases the field current, slowingthe motor Gd. Consumption of the positive carbon then causes the craterld to move to the right in. the ligure, causing more light to fall uponthe area of the photoconductive cell lil between terminals 2G and 2l andless to iall lil between terminals 24 and 26. Consequently theresistance between terminals 26 and 2l falls because oi' thephotosensitivity of the cell, while that between terminals 24 and 26rises, and as a result the potential of the control grid 34 appreachesthat of the cathode 32. The gas triode 33 consequently res later in eachpositive half cycle and its average anode current becomes less. Thisreduces the current drawn through the resistor 38 by the gas triode 33.However, this tube current flow is in the opposite direction to thelarger current ow in the same resistor due to the direct-current source39-39 so that the net current increases. Therefore, the voltage drop inthe resistor 38 increases, leaving less of the direct-current voltageavailable for the motor field 4i which accordingly is reduced instrength. 'lihis of course speeds up the motor 44 and iucreases the rateof advance ofthe positive carbon li, tending to restore the crater i4 toits correct position. This action continues until the crater l@ is fullyrestored to the correct position, when the two halves of the cell I9 areagain equally illuminated and the grid 34 is brought to its medialpotential. On the other hand, any deviation of the crater I4 to the leftfrom its correct position causes the opposite action, again resulting inrestoration of the crater to its correct position and maintenance of itthere.

in Fig. 2 there is depicted an embodiment of the invention employing ahot cathode gas discharge tube. This circuit has the advantage of beingsomewhat more sensitive to light variations and, in addition, the gridcurrent requirement is so low that the photoconductive cell can ifdesired be replaced by a phototube. The circuit is intended to replace aportion of the circuit oi Fig. l, electrical connection points 4l and 48and resistor 38 being similarly numbered. A hot cathode gas triode 49 isconnected for energizetion by the section 5i of the secondary windingvof a transformer 52, the anode 53 being connected to terminal il andthrough resistors 38 and 5U to the end terminal 54 of the winding 5i.The secondary midterminal 56 is connected to the cathode 5l. The heater58 is heated by current from a heater winding 59. Operation of thecontrol grid of a hot cathode gas tube is at about the voltage level ofthe cathode, therefore it is necessary to employ a second section ofsecondary winding (il connected to one diametral terminal of aphotoconductive cell 63, with the other diametral terminal 64 connectedto the anode terminal lil. The medial terminal 66 is then atapproximately the cathode potential level, and is connected to thecontrol grid 6l;

ln operation, when both halves of the cell 63 are equally illuminated anormal current iiows in the anode circuit of tube 49, when that half oithe cell included between the terminals tti and @il is illuminated morethan that included between the terminals 62 and Bil the grid 6l is mademore positive and more anode current iiows; while when that portionbetween 62 and il@ is illuminated more than the portion between 64 and@d the grid 6l ls made more negative and less anode current flows. Theaction through the coupling resistor 36 to control the motor dfi, Fig.l, is exactly as before described.

What is claimed is:

i. A control system for maintaining the electrode crater of an arc lampat a fixed position in space comprising, a pair of photosensitiveelements, means lor varying the relative illumination oi` saltiphotosensitive elements in accordance with the position of saidelectrode crater, a gas discharge tube, means interconnecting said pairof photosensitive elements and the electrodes of said gas discharge tubefor varying the grid cathode potential thereof in response to therelative illumination of said pair of photosensitive elements, a motorincluding a direct current iield connected to advance said arcelectrode, an alternating current circuit energizing the anode of saidgas discharge tube, a direct current circuit energizing said motorfield, said alternating current and direct current circuits including acommon series resistor.

2. A control system for maintaining the electrode crater of an arc lampat a fixed position in space comprising, a motor including a directcurrent winding connected to adjust' the position of said arc electrode,a pair of photosensitive elements positioned for illumination by saidarc crater, means interposed between said arc crater and said pair ofphotosensitive elements for varying the relative illumination thereof'in accordance with the position o! said arc crater, a gas dischargetube including at least anode, cathode and grid electrodes, saidphotosensitive elements being connected in series between said anode andcathode, and said grid electrode being connected to a common terminal ofsaid photosensitive elements, an alternating current circuit energizingthe electrodes of said gas discharge tube, a direct current circuitenergizing the direct current iield winding of said motor, and aresistor common t said alternating current and direct current circuits.

3. A control system for maintaining the electrode crater of an arc lampat a fixed position in space comprising, a motor including a directcurrent winding connected to advance said arc electrode at a ratedepending on the speed of said motor, a pair of photoconductiveelements, means for differentially illuminating said photoconductiveelements in accordance with the position of said electrode crater, a gasdischarge tube, means for varying the grid potential of said gasdischarge tube relative to the remainder of the electrodes thereof inaccordance with the relative differential illumination of saidphotoconductive elements, an alternating current circuit energizing theanode of said gas discharge tube, a direct current circuit energizingsaid motor field, said alternating current and said direct currentcircuits including a series resistor in common thereto.

4. A control system for maintaining the electrode crater of an arc lampat a iixed position in space comprising, a motor including a seriesdirect current winding connected to advance said arc electrode at a ratedepending on the speed ot said motor, a pair of photoconductive elementspositioned for illumination by said arc crater, means interposed betweensaid arc crater and said pair of photoconductive elements differentiallyilluminating said elements in accordance with the position of said arccrater, a gas discharge tube including at least anode, cathode and gridelectrodes, said photoconductive elements being connected in seriesbetween anode and cathode electrodes, and said grid electrode beingconnected to a common terminal of said photoconductive elements, analternating current energizing circuit connected between said cathodeand anode electrodes, a direct current circuit connected in series withsaid direct current motor winding, and a resistor common to saidalternating current and direct current circuit.

5. A control system for maintaining the electrode crater of an arc lampat a iixed position in space comprising, a motor including a seriesdirect current iield winding connected to advance said arc electrode ata rate depending on the speed of said motor, a pair of photoconductiveelements, means for differentially illuminating said photoconductiveelements in response to the position of said electrode crater, a gasdischarge tube including at least anode. cathode and grid electrodes,means varying the potential of said grid electrode in response to therelative differential illumination of said photoconductive elements, afirst circuit including a source of alternating current and a resistorconnected in series between said anode and cathode, a second circuitincluding a source of direct current and said resistor connected inseries with said motor field winding, said resistor constituting thesole element common to said lirst and second circuits.

6. A control system as dened in claim 5 in wligh said gas discharge tubeis a cold cathode tu 7. A control system as defined in claim 5 in viichsaid gas discharge tube is a hot cathode 8. A control system formaintaining the electrode crater of an arc lamp at a iixed position inspace comprising, a motor including a series direct current neld windingconnected to advance said arc electrode at a rate depending on the speedof said motor, a pair of photoconductive elements positioned forillumination by said arc crater, means interposed between said arccrater and said pair of photoconductive elements dinerentiallyilluminating said elements in accordance with the position of said arccrater, a gas discharge tube including at least anode, cathode and gridelectrodes, said photoconductive elements being connected in seriesbetween said anode and cathode electrodes, and said grid electrode beingconnected to a common terminal of said photoconductive elements. a iirstcircuit including a source of alternating current and a resistorconnected in series between said anode and cathode, a second circuitincluding a source of direct current and said resistor connected inseries with said motor field winding, said resistor constituting thesole element common to said first and second circuits.

9. A control system as deiined in claim 8 in which said gas dischargetube is a cold cathode tube and one of said photoconductive elements isdirectly connected to said cathode.

10. A control system as dened in claim 8 in which said gas dischargetube is a hot cathode tube and the cathode thereof is connected to oneof said photoconductive elements in seeswith a source of alternatingpotential.

RAYMOND L. GARMAN. JOHN K. MCKENDRY.

No references cited.

